Scanning devices using video cameras have been known and used in the past. Representative disclosures in the field include U.S. Pat. Nos. 3,505,465, 3,780,224, 3,868,706 and 4,024,573. U.S. Pat. No. 3,505,465 shows a viewing system for an armored vehicle in which incoming light is reflected from a convex mirror and reflected upwardly to a second convex mirror and then reflected downwardly to a television camera rotatably mounted in a housing. U.S. Pat. No. 3,780,224 shows a viewing system having three television cameras, all of which rotate in a housing with a mirror thereabove. U.S. Pat. No. 3,868,706 discloses a viewing system in which a television camera is secured to a rotatable turret which carries a mirror. The mirror rotates about a horizontal axis in the turret but the turret and mirror rotate with the television camera as a unit about a vertical axis. U.S. Pat. No. 4,024,573 discloses a viewing system in which a television camera is associated with a double dove prism mounted in front of the camera and rotatable by a drive motor.
In all the foregoing disclosures, the camera is rotated with the scanning reflector, and this limitation raises the problem of handling the electrical cables from the television camera to electronic circuitry including a television monitor for viewing the images represented by the video signals of the camera. Because of this problem, a need has arisen for an improved viewing system capable of scanning a field of view continuously in one direction about a vertical axis and at least within a limited angle about a horizontal axis.